GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 cutngs were analysed, and a contnuous spontaneous emission gamma log was measured. Accurate down-hole velocity measurements of both V P and V S were acquired, from the surface to the depth of 370 m, providing results in good match with a previous investgaton, which was limited in depth (Minarelli et al . 2016). The down-hole recordings were compared with the results of the vertcal seismic profle and of surface investgaton we performed on site, consistng of a seismic refecton profle, passive seismic arrays, and single-staton vibraton measurements. The various sources of informaton were combined to generate a reliable Vs profle and an interdisciplinary image of the subsurface propertes. Geology and Stratgraphy Framework The research region belongs to the external buried porton of the Apennines, dominated by actve thrust-fold structures (Martelli et al. , 2017), developed through Plio-Pleistocene tmes (Ghielmi et al ., 2013). The investgated site is placed on a broad syncline (Fig. 1A), part of the tectonic Ferrara Arc. The actve faults generate a signifcant seismic actvity, including that of May 2012. The strong synsedimentary deformaton largely infuenced the Plio-Quaternary stratgraphic architecture. The older unit involved in the research consists of Pliocene deep-marine terrigenous turbidites (P2, Fig. 3A). The interrupton of the turbidite sedimentaton in the study area (Porto Garibaldi Fm top) corresponds to the tectonic rising of submarine antcline bulges in western areas (e.g. Mirandola), preventng the currents from reaching eastern regions (Ghielmi et al. 2010, 2013). The following Marine Quaternary unit records the evoluton from deep-water argillaceous deposits (QM2) to delta sediments (QM1). The combinaton of tectonics, eustasy, and climate fuctuatons induced the unconformity surfaces supportng the subdivision of the following Quaternary successions into allostratgraphic units (Regione Emilia-Romagna et al. , 1998). A phase of deformaton induced the unconformity base of the Emilia-Romagna Supersynthem, which is bipartte into the Lower (AEI) and Upper (AES) Emilia-Romagna Synthems by a surface associated with a gentler phase of structural reorganizaton and marine lowstand (Martelli, 2021). At the study site, the lowermost porton of AEI stll records marine infuences, associated with interglacial highstand phases. The upper part of AEI and in AES record purely contnental conditons. The synthems in turn frame several subsynthems, each corresponding to an individual glacio-eustasy fuctuaton, in the 100,000-year frequency band, as in the upper three Subsynthems (AES 6, 7, 8). The research well crossed the whole of the Emilia-Romagna Supersynthem and penetrated a large porton of QM1. The propertes of the underlying units, down to the Pliocene turbidites (P2), were indirectly interpreted from the seismic investgaton we performed. Research methods and results In the research site, multple geophysical techniques were combined to achieve a reliable seismic wave propagaton model. The site was selected because placed in the epicentral area of the 2012 seismic sequence, and because of the availability of an accessible deep well, where a previous down-hole investgaton (Minarelli et al. , 2016) already measured both Vp and Vs velocites, to the depth of 265 m. We performed new accurate downhole measurements (Fig. 1B), to the depth of 370 m, together with passive and actve seismic surveys at the surface. Actve methods, performed by OGS authors, involved the data-acquisiton, in the S-waves mode, by geophones and hydrophones in the deep borehole, using a Mini-Vibratory (MiniVib) as source. First-break arrivals and refected waves were analysed to generate a 1D shear-wave velocity profle, analysed together with the refecton signals recorded by a linear patern of horizontal geophones, placed at the surface. Passive methods were also applied, through a high-resoluton frequency-wavenumber